Conventionally, as an optical communication line which is used as a trunk line for wiring an optical fiber from an accommodation line station to a subscriber's building or the like, a multi-core optical fiber cable is laid in the outdoor such as the air or the underground, or in the indoor. According to the line design of an optical communication line, it is often performed to connect multi-core optical fiber cables together, or to conduct a connection while branching one multi-core optical fiber cable into plural optical fiber cables. In a connecting portion in an outdoor environment such as the air or the underground, particularly, a closure for protecting the connecting point in consideration of the waterproof property and the like, or performing an extra-length treatment on an optical fiber is disposed.
Recently, in accordance with further popularization of the Internet, a request for introducing an optical fiber into a general household is being increased, and optical fibers of a reduced number of cores or one or two cores are branched from a multi-core optical fiber cable of a trunk line.
In the case where an optical fiber cable is introduced and branched in a building or an apartment building, when, after the optical fiber cable is passed through a vertical pipe, a branching process is to be performed by breaking the cable jacket, a work in a narrow space is required, and hence wiring is difficult to be performed. Alternatively, a cable to which a branching process is previously applied in a factory may be wired on the site. In this case, however, the process and the design are cumbersome, and the production cost and the like are increased.
As disclosed in Patent Reference 1, therefore, a technique is proposed in which a structure of an optical cable branch portion is employed in a branch portion protector. The structure comprises: a connector fixing portion for fixing an optical connector which terminates the tip end of an optical fiber drawn out from an optical cable so that it can be connected to an optical fiber on the side of a branch optical cable; and an extra-length housing portion which houses an extra length of the optical fiber.
Patent Reference 1: JP-A-2000-2811